Overview of the Telephone System
The station equipment and transmission facilities used by regional Bell operating companies (or "RBOCs") and other telephone service providers are well-known. FIG. 6 is a block diagram which illustrates the use of transmission facilities by various types of telecommunications services. As shown in FIG. 6, a number of geographically remote central switching offices 620a, 620b are coupled via "trunks" 614 and interoffice transmission facilities 618. Various entities, such as residences 602a, 602b, businesses 604a, 604b, and private branch exchanges (or "PBXs") 606a, 606b are coupled with a central switching office 620a, 620b via "lines" 610, 612 and "loop transmission facilities" 608.
Thus, a loop transmission facility (or "subscriber loop") 608 connects telecommunication equipment at a customer premises (e.g., a residence, business, etc.) with an associated central switching office 620a, 620b. The loop transmission facility 608 is typically on the order of a few miles and usually includes paired copper wire (also referred to as "twisted pair"). Interoffice transmission facilities 618, or trunks, connect different central switching offices 620a, 620b. Interoffice transmission facilities 618 range from less than one mile to thousands of miles.